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\section{Introduction}
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\label{sec:intro}
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In this note we describe a first study of isolated same sign (SS)
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and opposite sign (OS) low $P_T$ ($P_T > 10$ GeV)
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dileptons (e or $\mu$)
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in 7 TeV collision data. Our goal is to understand this
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data sample as a first step towards a top cross-section
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analysis~\cite{ref:topdil2009}, a $WW$ cross-section
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analysis~\cite{ref:WW}, as well as SS and OS SUSY
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searches\cite{ref:OSSusy}\cite{ref:SSSusy}.
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With a 10 GeV $P_T$ threshold, the data sample is dominated by QCD
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backgrounds and Drell-Yan events. We compare the observed yields
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with predictions from Monte Carlo. In the case of QCD, we use
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the Fake Rate method to predict its rate in a data driven way.
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With the present luminosity, there is not enough statistics to
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study kinematical distributions.
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This note is organized as follows. In Section~\ref{sec:datasets}
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we list the datasets used; the lepton identification criteria
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and the general event selection requirements
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are given in Section~\ref{sec:selection}; the event data yields are
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compared with Monte Carlo expectations in Section~\ref{sec:yields};
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the FR method is reviewed in Section~\ref{sec:FR}; the application
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of the FR method is summarized in Section~\ref{sec:FRapply}.
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{\color{red} This document was originally based on $\approx$ 10
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nb$^{-1}$ of integrated luminosity. It has now been partially
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updated to higher luminosity for ICHEP. Following instructions
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from the SUSY convenors, we leave the old results in the
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document. To facilitate reading, the document is color coded:
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\begin{itemize}
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\item everything in red is new
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\item everything in {\color{blue}blue} is old information that has been updated
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\item everything in {\color{black}black} is old information that has not
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been updated. In the case of plots and results, these would still be
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with the $\approx$ 10 nb$^{-1}$.
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\end{itemize}
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} |
